Mean Threshold Shift Research Articles

A combination antioxidant therapy prevents age-related hearing loss in C57BL/6 mice

Objective Age-related hearing loss (ARHL) is characterized by gradual, progressive sensorineural hearing loss, which impairs communication, lending to clinical depression and social withdrawal. There are currently no effective treatments for ARHL. The purpose of this study is to evaluate the potential of a combination antioxidant therapy in preventing ARHL. Study Design Randomized controlled trial. Setting Animal study. Subjects and Methods C57BL/6 mice, a recognized animal model of ARHL, were assigned to one of three groups: early treatment (n = 12), late treatment (n = 9), or control group (n = 9). Treatment groups of mice were fed with a combination agent comprising six antioxidant agents that target four sites within the oxidative pathway: L-cysteine-glutathione mixed disulfide, ribose-cysteine, NW-nitro-L-arginine methyl ester, vitamin B12, folate, and ascorbic acid. Auditory brainstem response (ABR) thresholds were recorded at baseline and every three months following initiation of treatment. Results Threshold shifts from baseline were decreased in the treatment groups when compared to the control group at all tested frequencies ( P < 0.001). The ABR threshold shift at 12 months of age for the control group was 34.7 dB with a 95% confidence interval (CI) of ±1.6. The mean threshold shifts for the early and late treatment groups were 7.5 dB (±0.87, 95% CI) and 9.2 dB (±1.6, 95% CI). Conclusion Combination antioxidant therapy effectively decreased threshold shifts on ABR within an animal model of ARHL. Combination antioxidant therapy, with further research and investigation, may provide a safe and cost-effective method of preventing presbycusis in the growing elderly population.

Ameliorative effects of an augmented acoustic environment on age‐related hearing loss in middle‐aged Fischer 344/NHsd rats

To investigate the effects of an augmented acoustic environment (AAE) on age-related hearing loss (ARHL) and outer hair cell (OHC) pathology in middle-aged Fischer 344/NHsd (F344/NHsd) rats. Eleven F344/NHsd rats were divided into two groups: 1) the AAE group (n = 5), which was exposed to 4-20 kHz broadband noise at 80 dB SPL for 12 h/d, 5 d/wk for 13 weeks starting from 16 months of age; and 2) the control group (n = 6), which did not receive the AAE during the same time span. Auditory brainstem response thresholds were obtained at different time points, and OHC pathology was examined after 13 weeks of AAE using propidium iodide and antiprestin antibody staining. The AAE-treated rats showed smaller mean threshold shifts (-1 to -3 dB) at 20-40 kHz than the control group (7.5-16.7 dB) at 13 weeks. No significant group differences were observed in the percentage of missing OHCs or abnormal OHC nuclei. However, examination of prestin in a pair of AAE and control rats revealed more uniform prestin staining intensity among OHCs in the AAE-treated cochlea than in the control cochlea. Thirteen-week AAE treatment in the middle-aged F344/NHsd rats slowed progression of ARHL. The AAE did not show a significant effect on OHC degeneration, but it is speculated that the AAE may maintain the integrity of prestin to preserve OHC functionality. However, further study is warranted to understand the protective mechanism of AAE as an intervention against ARHL.

Loss of GABAB Receptors in Cochlear Neurons: Threshold Elevation Suggests Modulation of Outer Hair Cell Function by Type II Afferent Fibers

Despite pharmacological and immunohistochemical evidence for GABA as a neurotransmitter in the olivocochlear efferent bundle, a clear functional role of GABA in the inner ear has not emerged. To explore the role of metabotropic GABA(B) receptors, we characterized the cochlear phenotype of mice with targeted deletion of the GABA(B1) subunit and determined its tissue localization using a mouse line expressing a GFP-tagged GABA(B1) subunit under the endogenous promoter. Immunostaining revealed GABA(B1) expression in both type I and type II ganglion cells and in their synaptic terminals under inner and outer hair cells, respectively. No GABA(B1) expression was observed in hair cells. Mean cochlear thresholds, measured via both auditory brainstem responses and distortion product otoacoustic emissions (DPOAEs), were elevated by approximately 10 dB in GABA(B1)-deficient mice, consistent with outer hair cell dysfunction. Olivocochlear efferent function, assessed via DPOAE suppression during efferent electrical stimulation, was unaffected by GABA(B1) deletion. GABA(B1)-deficient mice showed increased resistance to permanent acoustic injury, with mean threshold shifts approximately 25 dB smaller than wild-types after exposure to 8-16-kHz noise at 100 dB for 2 h. In contrast, there was no vulnerability difference to temporary acoustic injury following exposure to the same noise at 94 dB for 15 min. Our results suggest that GABAergic signaling in type II afferent neurons may be required for normal outer hair cell amplifier function at low sound levels and may also modulate outer hair cell responses to high-level sound.

Evolution of Audiometric Pattern in Meniere’s Disease: Long-Term Survey of 380 Cases Evaluated According to the 1995 Guidelines of the American Academy of Otolaryngology-Head and Neck Surgery

Hearing loss in the early stages of Meniere's disease is characterized by a fluctuation in the audiometric pattern limited to the low frequencies, and then, during the disease's evolution, the hearing loss involves the medium and high frequencies. As far as the prevalence of different types of audiometric curves is concerned, there is no agreement among the various studies. The study of audiometric evolution in the course of the disease has been limited owing to the difficulties in following a relevant number of patients for a long period of time. The aim of the present study was to compare the auditory level and audiometric pattern evolution in a significant number of patients suffering from Meniere's disease who had undergone long-term follow-up (at least 10 years). The study considered 380 patients with a confirmed diagnosis of Meniere's disease. The audiometric data were collected at the onset of the disease and after 5 and 10 years. Four patterns were considered: peak, rising, falling, and flat. Audiometric evolution analysis in four stages, defined by the guidelines of the American Academy of Otolaryngology-Head and Neck Surgery, was evaluated. At the onset, in 190 cases, the audiometric pattern was a peak curve, with fluctuation of the threshold in 68% of cases. The mean threshold shift for the 500 to 3000 Hz range was between 26 and 40 dB. After 5 years, a peak type (41.9%) or a flat type (42.9%) was observed; the pure-tone average (PTA) ranged between 26 and 40 dB in 47.9% and between 41 and 70 dB in 51.8% of cases. After 10 years, in most cases (57.9%), a flat curve was observed, and the PTA in 100% ranged between 41 and 70 dB. The most common audiometric pattern at the onset of the disease is the peak type; long-term transformation of the initial audiometric pattern into a flat curve has been confirmed. High-frequency involvement seemed to be related more to Meniere's disease duration than to the influence of aging on hearing loss.

Underwater temporary threshold shift in pinnipeds: Effects of noise level and duration

Behavioral psychophysical techniques were used to evaluate the residual effects of underwater noise on the hearing sensitivity of three pinnipeds: a California sea lion (Zalophus californianus), a harbor seal (Phoca vitulina), and a northern elephant seal (Mirounga angustirostris). Temporary threshold shift (TTS), defined as the difference between auditory thresholds obtained before and after noise exposure, was assessed. The subjects were exposed to octave-band noise centered at 2500 Hz at two sound pressure levels: 80 and 95 dB SL (re: auditory threshold at 2500 Hz). Noise exposure durations were 22, 25, and 50 min. Threshold shifts were assessed at 2500 and 3530 Hz. Mean threshold shifts ranged from 2.9-12.2 dB. Full recovery of auditory sensitivity occurred within 24 h of noise exposure. Control sequences, comprising sham noise exposures, did not result in significant mean threshold shifts for any subject. Threshold shift magnitudes increased with increasing noise sound exposure level (SEL) for two of the three subjects. The results underscore the importance of including sound exposure metrics (incorporating sound pressure level and exposure duration) in order to fully assess the effects of noise on marine mammal hearing.

Are hearing sensitivities of freshwater fish adapted to the ambient noise in their habitats?

Several groups of fishes, among them two thirds of all freshwater fishes, have developed hearing specializations that enhance auditory sensitivity and broaden frequency ranges compared with hearing non-specialists (generalists), which lack such adaptations. It has been speculated that the enhanced sensitivities of these so-called hearing specialists have evolved in quiet habitats such as lakes, backwaters of rivers, slowly flowing streams or the deep sea. To test this hypothesis, noise levels and frequency spectra of four different freshwater habitats near Vienna, Austria (Danube River, Triesting stream, Lake Neusiedl, backwaters of the Danube River), were recorded and played back to native fish species while simultaneously measuring their auditory thresholds using the auditory evoked potential (AEP) recording technique. As a representative of hearing specialists, we chose the common carp (Cyprinus carpio, Cyprinidae) and for the hearing generalists the European perch (Perca fluviatilis, Percidae). Data show that the carp's hearing is only moderately masked by the quiet habitat noise level of standing waters (mean threshold shift 9 dB) but is heavily affected by stream and river noise by up to 49 dB in its best hearing range (0.5-1.0 kHz). In contrast, the perch's hearing thresholds were only slightly affected (mean up to 12 dB, at 0.1 kHz) by the highest noise levels presented. Our results indicate that hearing abilities of specialists such as carp are well adapted to the lowest noise levels encountered in freshwater habitats and that their hearing is considerably masked in some parts of their distribution range. Hearing in non-specialists such as perch, on the other hand, is only slightly or not at all impaired in all habitats.

Effects of Alcohol and Noise on Temporary Threshold Shift in Guinea Pigs

The purpose of this study was to investigate the effects of concomitant exposure to noise and alcohol on the auditory thresholds. Twenty-four guinea pigs were equally divided into three groups: the acute intoxication group, the chronic intoxication group and the control group. Animals in the acute group received single intraperitoneal injections of ethanol (2 g/kg). In the chronic group, alcohol was administered via drinking water (10%, v/v) over a 60-day period. All animals were exposed to a white noise at the intensity of 105 dB A for 30 min. Auditory brainstem response (ABR) thresholds and distortion product otoacoustic emission (DPOAE) levels were measured before, immediately after noise exposure and also 1, 2, and 7 days following exposure. The results showed: first, acute alcohol injection caused a significant, temporary elevation of ABR threshold (4.8 dB in average), while chronic alcohol treatment did not change auditory threshold significantly. Second, noise exposure induced a mean threshold shift of 15.4– 19.7 dB. ABR threshold returned to normal 2 days after exposure. Both acute and chronic alcohol treatment did not alter the magnitude and time course of recovery of the temporary threshold shift (TTS). Third, the mean DPOAE amplitudes decreased at most frequencies following acute injection of alcohol. However, the differences did not reach statistical significance. Fourth, the mean DPOAE levels dropped 3.4–9.6 dB in all groups after noise exposure and returned to normal 1 day to 2 days after noise. There were no significant differences in the amount of DPOAE suppression after noise between the three groups. In summary, we have found that acute and chronic treatment of alcohol in combination with noise did not significantly exacerbate TTS or decrease DPOAE amplitudes relative to noise exposure alone.

Cisplatin Ototoxicity in the Sprague Dawley Rat Evaluated by Distortion Product Otoacoustic Emissions:Ototoxicidad por Cisplatino en la rata Sprague Dawley evaluada mediante productos de distorsión de las emisiones otoacústicas

The present study has evaluated the use of distortion product otoacoustic emission (DPOAE) responses in the detection of cisplatin-induced ototoxicity in a Sprague Dawley rat animal model. The cisplatin was administered as a 16 mg/kg, dose introduced by a slow 30-min intraperitoneal infusion. Data from three DP-gram protocols, DPOAE input-output responses at 8 kHz, and auditory brainstem responses (ABRs) at 8, 12 and 16 kHz were collected before and 72 h after treatment. The post-treatment ABRs at 16 kHz showed the greatest mean threshold shift of 33.6 dB. The post-treatment DP-gram data showed significant reduction of the signal to noise ratios in the majority of the frequencies tested, across all tested protocols. The data suggest that the most sensitive DPOAE procedure for the early detection of the cisplatin-induced ototoxic damage is the DPOAE I/O protocol. Morphological analyses indicated that the inner hair cells remained intact, while several types of alterations were observed in the arrangement o...

Pharmacological protection of auditory function against noise and hypoxia with MK 801

INTRODUCTION: Pharmacological protection of cochlear function is one of the most exciting goals of inner ear medicine. The selective glutamate antagonist MK 801 may be neuro-protective to the cochlea.1 This study aims to investigate whether round window administration of MK 801 protects cochlear function against a combination of noise and atmostpheric hypoxia. METHODS: Eight guinea-pigs were studied. Round Window E. Catheters (Durect Inc., USA) were implanted through a trans-bulla approach and EcoG thresholds determined at 8, 16, 24 and 30 kHz. Artificial perilymph (n = 4) or 10 mM MK 801 (n = 4) was then perfused onto the round window membrane. After 15 min the anaesthetized animals were exposed to 100 dB white noise in 11.5-12. 5% atmospheric oxygen. Thresholds were determined before and 15 min after exposure. RESULTS: The mean threshold shifts from pre-perfusion at 8, 16, 24 and 30 kHz were 40, 33, 35 and 17 dB, respectively (in control animals) and 29, 28, 33 and 41 dB, respectively (in treated animals). A marginal protective effect was demonstrated at 8 kHz (P = 0.06). The 30-kHz thresholds in the treated group fell by 61 dB before noise exposure compared to < 1 dB in the controls (P = 0.0007), suggesting that at high frequencies, 10 mM MK 801 may itself be ototoxic. CONCLUSIONS: These results partially support existing data suggesting that pharmacological protection against noise/hypoxia is possible. Administration of round window NMDA antagonists may affect normal auditory threshold making detailed evaluation of the toxicity of potential inner ear therapies essential before clinical use is contemplated.

Stapedotomy in osteogenesis imperfecta patients.

Osteogenesis imperfecta (OI) is a connective tissue disorder characterized by osseous fragility, blue sclerae and hearing loss. In order to assess the impact of stapedotomy on improving hearing on OI, a retrospective, one-group, pre-test-post-test design was used to compare the pre-operative and post-operative audiograms of nine OI patients, treated with stapedotomy for their mixed hearing loss. Operative findings included fixation or thickening of the stapes footplate with normal superstructure configuration and hypervascularization of the promontory mucosa. Immediate post-operative results showed a significant improvement (p < 0.05) from 250-4000 Hz in air conduction and from 250-2000 Hz in bone conduction. A significant closure of the air-bone gap between 250-2000 Hz was also achieved (p < 0.05). The long-term results remained satisfactory with a mean threshold shift of 8 dB HL and an almost unchanged air-bone gap. These satisfactory results and the lack of complications make stapedotomy an appealing method for the management of OI-associated hearing loss.

Temporary threshold shift in pinnipeds induced by octave-band noise in water

Low-frequency noise from manmade sources represents an increasing portion of the total noise in the ocean. Such noise may adversely impact diving pinnipeds, which hear relatively well at low frequencies. The effects of octave bands of moderately intense noise (under 4 kHz, 60–76 dB SL, 20–22 min duration) were examined in three species of pinniped, the California sea lion (Zalophus californianus), harbor seal (Phoca vitulina), and northern elephant seal (Mirounga angustirostris). Auditory sensitivity data were obtained behaviorally, using a go/no-go psychophysical procedure. Thresholds were determined before noise exposure, immediately after noise exposure, and again after 24 h. Mean threshold shifts ranged from 2.9–4.9 dB at the center frequency of the noise band. Recovery was complete after 24 h. These results show that noise levels as low as 60 dB SL can induce TTS. However, between 60 and 76 dB SL, there was no relationship between noise level and degree of TTS. Additionally, maximum hearing loss occurred at center frequency rather than one-half octave above the center frequency. Further testing at longer exposure durations and higher noise levels is needed to more completely assess the degree to which pinniped underwater hearing is affected by continuous noise exposure.

R-phenylisopropyladenosine attenuates noise-induced hearing loss in the chinchilla

Reactive oxygen species, which are cytotoxic to living tissues, are thought to be partly responsible for noise-induced hearing loss. In this study R-phenylisopropyladenosine (R-PIA), a stable non-hydrolyzable adenosine analogue which has been found effective in upregulating antioxidant enzyme activity levels, was topologically applied to the round window of the right ears of chinchillas. Physiological saline was applied to the round window of the left ears (control). The animals were then exposed to a 4 kHz octave band noise at 105 dB SPL for 4 h. Inferior colliculus evoked potential thresholds and distortion product otoacoustic emissions (DPOAE) were measured and hair cell damage was documented. The mean threshold shifts immediately after the noise exposure were 70–90 dB at frequencies between 2 and 16 kHz. There were no significant differences in threshold shifts at this point between the R-PIA-treated and control ears. By 4 days after noise exposure, however, the R-PIA-treated ears showed 20–30 dB more recovery than saline-treated ears at frequencies between 4 and 16 kHz. More importantly, threshold measurements made 20 days after noise exposure showed 10–15 dB less permanent threshold shifts in R-PIA-treated ears. The amplitudes of DPOAE also recovered to a greater extent and outer hair cell losses were less severe in the R-PIA-treated ears. The results suggest that administration of R-PIA facilitates the recovery process of the outer hair cell after noise exposure.

Interaction of noise-induced permanent threshold shift and age-related threshold shift

Current medical-legal practices as well as an international standard (ISO 1999) assume the permanent threshold shifts produced by exposure to noise add (in dB) to the threshold shifts caused by increased chronological age (presbyacusis). This assumption, known as the additivity rule, was tested in an animal model. Mongolian gerbils, born and raised in a quiet vivarium, were exposed at age 18 months to a 3.5-kHz pure tone for 1 h at 113 dB SPL. At 6-weeks post-exposure, permanent threshold shifts in the exposed ear were approximately 20 dB in the 4- to 8-kHz region. Thresholds in the nonexposed, control ear were unaffected by the exposure. Animals were then allowed to age in the quiet vivarium until age 36 months and then were retested. Thus in a given animal, aging-only effects were assessed in one ear (internal control) and noise-plus-aging effects were assessed in the other (test) ear. A second control was mean age-related threshold shift measured in 48 gerbils who were born and raised in the quiet vivarium. This group is referred to as a non-noise-exposed population (population control). Using the additivity rule, predictions with either the internal or population control significantly overestimated noise-plus-aging effects. Use of the ISO 1999 compression factor reduced the overestimations by 0-5 dB. The intensity rule produced the most accurate predictions. These results suggest that the interaction of noise-induced permanent threshold shift and age-related threshold shift is not straightforward and that current medical-legal methods using the additivity rule overestimate the contribution of "noise effects".

Repetition enhances hearing detection thresholds in a harbour seal (Phoca vitulina)

Pure-tone hearing thresholds of a harbour seal (Phoca vitulina) were measured in air and underwater using behavioural psychophysical techniques. A 50-ms sinusoidal pulse was presented in both white-noise masked and unmasked situations at pulse repetition rates of 1, 2, 4, and 10/s. Test frequencies were 0.5, 1.0, 2.0, 4.0, and 8.0 kHz in air and 2.0, 4.0, 8.0, and 16.0 kHz underwater. Relative to 1 pulse/s, mean threshold shifts were −1, −3, and −5 dB at 2, 4, and 10 pulses/s, respectively. The threshold shifts from 1 to 10 pulses/s were significant (F = 12.457, df = 2,36, p &lt; 0.001) and there was no difference in the threshold shifts between the masked and unmasked situations (F = 2.585; df = 1,50; p &gt; 0.10). Broadband masking caused by meteorological or industrial sources will closely resemble the white-noise situation. At high calling rates, the numerous overlapping calls of some species (e.g., harp seal, Phoca groenlandica) present virtually continous "background noise" which also resembles the broadband white-noise masking situation. An implication of lower detection thresholds is that if a seal regularly repeats short vocalizations, the communication range of that call could be increased significantly (80% at 10 pulses/s). This could have important implications during the breeding season should storms or shipping noises occur or when some pinniped species become increasingly vocal and the background noise of conspecifics increases.

Middle ear disease in young children with sensorineural hearing loss.

Early identification of children with sensorineural hearing loss (SNHL), coupled with the provision of appropriate conventional amplification constitute important elements of a (re)habilitative strategy. Often overlooked, however, is the problem posed by recurrent and chronic middle ear disease in the child with coexisting SNHL. This study focuses on 437 (237 boys and 200 girls) consecutive patients with bilateral SNHL, in the moderate range or poorer, who were diagnosed prior to age 5 years at Boys Town National Research Hospital. The mean threshold shift with effusion was 25.0 dB at 250 Hz, 28.5 dB at 500 Hz, 29.5 dB at 1000 Hz, 24.5 dB at 2000 Hz, and 27.5 dB at 4000 Hz. During a median follow-up period of 3.21 years, 154 (35.2%) of these children required surgical placement of tympanostomy tubes because of the severity of middle ear disease and its impact on auditory acuity. Accurate determination of the degree and audiologic configuration of a SNHL may be seriously hindered by a coexisting middle ear effusion. If initial findings indicate the presence of a middle ear effusion, measures of auditory function must be repeated after the effusion has been resolved by medical and/or surgical intervention.

Directional dependence of auditory sensitivity and frequency selectivity in the leopard frog

Direction-dependent changes in frequency selectivity were documented in three populations of neurons in the auditory periphery of the leopard frog: low-, mid-, and high-frequency sensitive fibers. These changes were most pronounced in the mid-frequency (720-1199 Hz) sensitive fibers which exhibited positive shifts in characteristic frequencies (CFs) and concomitant narrowed bandwidths from posterior speaker presentations. Maximum sensitivities were observed for ipsilateral speaker presentations in these fibers. Low-frequency (63-500 Hz) sensitive fibers exhibited mean threshold shifts at their CFs of up to -7 dB with posterior speaker presentations. Low- and high-frequency sensitive fibers whose CFs closely correspond to the peaks of spectral energy of the species' mating call were the most sensitive (exhibited lowest thresholds) but showed little directional-dependent frequency selectivity. Directional-dependent variation in frequency selectivity and sensitivity in low- and mid-frequency sensitive fibers was attributed to pressure and phase differences impinging on the inner surface of the eardrum.

Effects of ambient noise masking on earphone thresholds.

Monaural thresholds were measured for 24 normally hearing subjects using TDH-49P, Audiocup, and ER-3A earphones from 500 to 6000 Hz in quiet and in background noise having maximum permissible ambient noise levels (MPANLs) specified by OSHA (1983) and ANSI (S3.1-1991). The attenuation for each earphone system was obtained and the actual threshold shift was compared to the predicted threshold shift. The mean threshold shifts were negligible (≤2 dB) in the ANSI MPANLs regardless of earphone and in OSHA MPANLs for the ER-3A but ranged from 2 to 7.5 dB for the Audiocup and from 6 to 12.5 dB for the TDH-49P in the OSHA MPANLs. The results of this study suggest that OSHA MPANLs are too high to allow for testing down to 0-dB HL using these earphones. The high noise-reducing properties of the ER-3A would make it the earphone of choice if testing is done in OSHA MPANLs. Testing down to 0 dB HL can be done in the newly specified ANSI MPANLs regardless of earphone type.

Middle ear muscle effects during gunfire noise exposures

A previous study using evoked response audiometry in anesthetized cats [Price and Wansack, J. Acoust. Soc. Am. 86, 2185 (1989)] showed that an impulse with its peak energy in the 4.0-kHz region was surprisingly hazardous. The surprisingly great effect could have been due to the anesthesia itself or the anesthesia could have prevented middle ear muscle contractions (normally not thought to affect the ear's response to gunfire). In order to help discriminate, three groups of ten cats were exposed to 50 midrange impulses at 145 dB peak, fired 3–5 s apart. Group I was anesthetized at the time of the exposure, and groups II and III were not; however, group II was anesthetized for threshold testing immediately after exposure (measured by evoked response audiometry at 2.0, 4.0, 8.0, and 16.0 kHz). Mean threshold shifts at 4.0 kHz 20–30 min post-exposure were 72 dB for group I and 19 dB for group II. Permanent threshold shifts were 44 dB for group I and 5.9 and 5.3 dB for groups II and III, respectively. These data suggest that the anesthetic itself probably does not potentiate the exposure and that the middle ear muscles should be suspected as being protective in any waking cat.

Reversible Conductive Hearing Loss in Mice

Fibrin tissue adhesive was injected into the right ears of four 7-week-old CBA/J mice. Auditory brain stem responses (ABRs) were used to monitor changes in auditory sensitivity over the next 26 days, after which the middle ears and cochleas were examined histologically. Mean maximum ABR threshold shifts were as great as 36 dB, and were larger for higher frequencies than for lower. Maximum shifts occurred between 1 and 8 days; by 26 days, thresholds had returned to intensity levels observed before injection.

Auditory temporal summation in normal‐hearing and hearing‐impaired cat

Auditory temporal summation functions were measured for five cats before and after they were exposed to a 2‐kHz tone at 110 dBA for 48 h. Ten digitally generated stimuli with overall durations ranging from 8.32 to 275 ms were used. Stimulus frequency was 6.25 kHz. Six stimuli consisted of single tone bursts and the remaining four contained multiple tone bursts. Twelve acceptable thresholds for each stimulus were obtained from each animal before and after exposure. Threshold measurements began again no sooner than 27 days postexposure. Pre‐ and postexposure audiograms were also obtained and mean permanent threshold shift at 6.25 kHz was 32.6 dB. Pre‐ and postexposure temporal summation functions were characterized by the slope of the regression lines for threshold versus log duration. The mean slope in dB per decade of duration was − 6.6 preexposure and − 3.8 postexposure. The slope for normal‐hearing cat is very similar to the slope of − 6.1 that was obtained in a companion study that used normal‐hearing human subjects.